The invention relates to a process for preventing burn-off on peripheral surfaces of a current-conducting electrode for metallurgical surfaces, which comprises a durable upper part and a consumable tip and which is cooled in the upper part, as well as a current-conducting electrode for performing the process.
It is conventional practice to use graphite or carbon electrodes for operating metallurgical furnaces, e.g. electric furnaces for smelting steel scrap. However, as the electrodes are subject to continuous burn-off during smelting, they must periodically be at least partly replaced. The raw materials for producing such electrodes are becoming increasingly scarce and are also subject to continuous price increases, so that the electrode cost proportion in metallurgical processes is correspondingly increasing.
In the case of arc furnaces, for example, the consumption of graphite electrodes is as follows. Of the total consumption, approximately 50% is burn-off of the electrode tip, approximately 45% lateral electrode burn-off and approximately 5% losses by electrode waste.
Numerous efforts have been made to reduce the consumption of graphite electrodes. As tip burn-off is due to the operation of the furnace, these efforts have mainly been directed at reducing lateral burn-off. Electrodes are known in which the upper part is made from a metal, e.g. a copper tube cooled by a cooling medium, instead of being made from graphite. A consumable graphite tip is fixed to this upper part by means of a graphite or metal thread nipple. The metal electrode portions of the upper part have the disadvantage that they are subject to higher thermal losses and there is a risk of burn-through on contact with conductive parts, e.g. steel scrap. To avoid the latter disadvantage, it has been proposed to peripherally electrically insulate the metal electrode portions. The known insulants used for this do not, however, have an adequate durability. A further disadvantage is that such metal electrode portions can only be secured with difficulty in conventional electrode holders and problems occur when power is supplied.
It is also known to coat or impregnate the graphite electrode portions to prevent lateral burn-off. However, both processes are very complicated and costly. In addition, problems can occur in the electrode holder when supplying power.
The problem of the present invention is therefore to further develop a process of the aforementioned type that a considerable reduction of lateral burn-off can be achieved with acceptable expenditure and effort, without modifying the external shape of the electrode or providing additional measures.